Recent reports from scientists studying a new kind of fusion technology are encouraging, but we are still some distance from the 'holy grail of clean energy'.
The technology, developed by Heinrich Hora and his colleagues at the University of New South Wales, uses powerful lasers to fuse hydrogen and boron atoms, releasing high-energy particles that can be used to generate electricity.
However, as with other types of fusion technology, the challenge lies in creating a machine that can reliably initiate a reaction and use the energy it produces.
What is fusion energy?
Fusion is the process that powers the sun and stars. This happens when the nuclei of two atoms are so close to each other that they combine into one, releasing energy in the process.
If the reaction can be replicated in the laboratory, it can provide virtually unlimited baseload power with virtually zero carbon footprint.
The simplest reaction that can be initiated in a laboratory is the fusion of two different isotopes of hydrogen: deuterium and tritium. The reaction product is a helium ion and a fast moving neutron. Most synthesis studies to date have pursued this reaction.
Deuterium-tritium fusion works best at around 100,000,000 ℃. Plasma confinement is the name given to the flame-like state of matter at these temperatures.
The leading approach to using fusion forces is called toroidal magnetic confinement. Superconducting coils are used to create a field about a million times stronger than the Earth's magnetic field to contain the plasma.
Scientists have already achieved deuterium-tritium fusion in experiments in the USA (test reactor for fusion in Tokamak) and the UK (United European Torus). Indeed, this year a British experiment will be running a deuterium-tritium fusion campaign.
These experiments initiate a fusion reaction using massive external heating, and it takes more energy to sustain the reaction than the reaction itself produces.
The next phase of major merger research will include an experiment called ITER (Latin for 'path') to be built in the south of France. In ITER, the limited helium ions produced by the reaction will produce as much energy as external sources. Since a fast neutron carries four times as much energy as a helium ion, the power will increase five times.
What is the difference between the use of hydrogen and boron?
The technology, reported by Hora and his colleagues, involves the use of a laser to create a very strong confining magnetic field and a second laser to heat the hydrogen fuel pellet to reach the flash point.
When a hydrogen nucleus (one proton) fuses with a boron-11 nucleus, three helium energy nuclei are formed. Compared to the deuterium-tritium reaction, the advantage is that there are no neutrons that are difficult to contain.
Hora's solution is to use a laser to heat a small fuel pellet to its ignition temperature and another laser to heat the metal coils to create a magnetic field that will contain the plasma.
The technology uses very short laser pulses, only nanoseconds in duration. The required magnetic field would be extremely strong, about 1000 times stronger than the field used in experiments with deuterium and tritium.
Hora and colleagues argue that their process will create an 'avalanche effect' in the fuel pellet, which means a lot more fusion will take place than would be expected.
Although there is experimental evidence to support a slight increase in fusion reaction rate by adapting the laser beam and target, for comparison with deuterium-tritium reactions, the avalanche effect would have to increase the fusion reaction rate by over 100,000 times at 100,000,000 ℃.
The experiments with hydrogen and boron have certainly produced exciting physical results, but the predictions of Hora and colleagues about a five-year path to realizing thermonuclear energy seem premature. Other scientists have already tried to launch laser fusion. For example, they tried to achieve ignition from hydrogen-deuterium fusion using 192 laser beams focused on a small target.
These experiments reached one third of the conditions required for one experiment. Problems include precise target positioning, laser beam irregularities and instability caused by explosions.
The development of thermonuclear energy will most likely be implemented by the main international program, which is based on the ITER experiment. Australia has international cooperation with the ITER project in the fields of theory and modeling, materials science and technology.
Matthew Hole, Senior Research Fellow, Institute of Mathematical Sciences, Australian National University.
This article was published by The Conversation.
Sources: Photo: CCFE / JET
